New Polymer Mix Crafts More Efficient Solar Cells

The new device, developed by a team from the University of Chicago’s Institute for Molecular Engineering in collaboration with Argonne National Laboratory, employs a new polymer, PID2, in addition to the standard polymer-fullerene mix found in some solar cells.

The new polymer produces electrical charges that allow it to move more easily throughout a solar cell, thus boosting the production of electricity.

The new PID2 polymer, when added to a standard polymer-fullerene mixture, has shown to improve efficiency of power generation. Images courtesy of University of Chicago.
Added to a standard polymer-fullerene mixture, PID2 has been shown to improve the efficiency of polymer cells’ electrical power generation.

“In polymer solar cells we have a polymer as electron donor and fullerene as electron acceptor to allow charge separation,” said Luyao Lu, graduate student in chemistry at UChicago.

In the study, introduction of the PID2 to the device essentially resulted in solar cells with two polymers and one fullerene, which demonstrated an efficiency of 8.22 percent. The standard mechanism for improving efficiency with a third polymer is by increasing the absorption of light in the device.

In order for an electric current to be generated by the solar cell, electrons must be transferred from polymer to fullerene within the device. However, the researchers found that the difference between electron energy levels for the standard polymer-fullerene is large enough that electron transfer between them is difficult. PID2 has energy levels in between the other two polymers, and acts as an intermediary in the process.

Chemist Luyao Lu works to develop a new type of polymer solar cell that displays enhanced power conversion efficiency.
The addition of PID2 ultimately caused the polymer blend to form fibers, which improved the mobility of electrons throughout the material. These fibers served as a pathway to allow electrons to travel to the electrodes on the sides of the solar cell, according to the researchers.

The team is continuing its study, pushing for even higher efficiencies. Reaching 10 percent would allow polymer solar cells to be viable for commercial application, they said.

“This knowledge will serve as a foundation from which to develop high-efficiency organic photovoltaic devices to meet the nation’s future energy needs,” said Wei Chen, a researcher at UChicago and an assistant chemist in the Materials Science Division at Argonne Lab.

The work was funded by the National Science Foundation, the U.S. Air Force Office of Scientific Research, and the U.S. Department of Energy.